There have been numerous processes previously proposed for the manufacture of alkaloid carbonate, various sulfates, etc. One of the primary difficulties with the known procedures for manufacturing, for example, sodium bicarbonate and ammonium sulfate is the fact that a pure product is difficult to obtain when one employs the methods previously set forth in the art.
Typical of the previously proposed methods includes that taught in Canadian Patent No. 543107, issued Jul. 2, 1957, to Downes. The reference teaches a method of separating polybasic acids from their aqueous solutions and the recovery of ammonium sulfate from aqueous solutions. The disclosure indicates that the treatment of sodium sulfate for the production of sodium bicarbonate and ammonium sulfate may be achieved by exposing the aqueous solution of sulfate to ammonia and carbon dioxide. The result is the precipitation of sodium bicarbonate. Although the Downes method is useful to recover the sodium bicarbonate, there is no teaching in the disclosure concerning how an uncontaminated product of sodium bicarbonate and ammonium sulfate, since these are reciprocal salt pairs capable of formation of a double salt by following the method. In addition, the method as set forth in this reference would appear to be susceptible to the formation of hydrates one being known as Glauber salt when using these salt pairs.
Stiers, in U.S. Pat. No. 3,493,329, issued Feb. 3, 1970, teaches a method of making sodium carbonate. The Stiers method is a co-precipitation method and cannot provide for selective precipitation of desired products since the salts are reciprocal salts and form a double salt. In the Stiers method, the desire is to remove the sulfate anion to use it for the transportation of sodium cations from sodium chloride to the bicarbonating process as sodium sulfate. In addition to the above, the Stiers process involves the continuous recycling of the mother liquor which requires that the ammonium sulfate in the liquor be continuously removed or reduced from the process stream. If the ammonium sulfate reaches a saturation point in the bicarbonating stage, ammonium sulfate will co-precipitate with the sodium sulfate in the form of a double salt compound or two inseparable salts.
Stiers demonstrates a process to generate two salts and double salts rather than a pure single salt, the latter being much more desirable from a commercial point of view.
In view of what has been Previously proposed in the art, it is clear a need exists for a process of recovering sodium carbonate compounds and the formation ammonium sulfate from a source of sulfate which overcomes the limitations regarding purity, precipitation, selectivity and other such limitations. The present invention is directed to circumventing the previously encountered difficulties of reciprocating salt pairs.
It is clear that there has been a long felt need for an effective process for preparing ammonium sulfate as a substantially uncontaminated product from reciprocating salt pairs.